1. Field of the Invention
The present invention relates to a resin composition for production of an optical waveguide, and to an optical waveguide produced by using the resin composition.
2. Description of the Related Art
An optical waveguide typically includes a core portion and a cladding portion. With a difference in refractive index between the core portion and the cladding portion, the core portion serves as a light passage for transmission of a light signal. Exemplary materials for conventional optical waveguides include inorganic materials such as quartz glass and silicon, and organic materials such as highly pure polyimide resins, polyamide resins and polyether resins.
In recent years, various optical waveguide production methods have been developed, in which a photosensitive resin solution (photosensitive monomer mixture solution) is used as an optical waveguide material, and the core portion of the optical waveguide is formed by forming a coating layer of the solution and photo-curing the coating layer by irradiation of the coating layer with ultraviolet radiation via a mask of a predetermined pattern for easy production of the optical waveguide (see, for example, JP-A-2001-281475).
However, the photosensitive resin solution conventionally used in the aforementioned application has a higher photo-curing sensitivity, and the coating layer (uncured layer) of the photosensitive resin solution has a tacky surface (or has surface tackiness). This makes it difficult to employ a continuous process such as a roll-to-roll process using a multi-coater or a like coating machine. In the roll-to-roll process, the coating layer is wound up to be brought into contact with a previously wound portion thereof, whereby the previously wound portion and the newly wound portion of the coating layer adhere to each other. This may result in breakage of the adhering portions of the coating layer.
Where the roll-to-roll process is employed for the formation of the coating layer, a so-called “ordinary-temperature solid polymer resin” which is in a solid phase at an ordinary temperature is used for the photosensitive resin solution (see, for example, JP-A-2005-154715).
Where the aforementioned ordinary-temperature solid polymer resin to be used has a higher molecular weight, however, an uncured layer of the resin (an amorphous film before the curing) has higher flexibility, but disadvantageously has lower patterning resolution. If the resin has a lower molecular weight, on the other hand, the patterning resolution is higher, but the flexibility is lower.
Thus, there is a trade-off relationship between the flexibility and the patterning resolution of the uncured layer. For this reason, an optical waveguide material suitable for the roll-to-roll process including the winding step is not provided yet. Accordingly, there is an eager demand for an optical waveguide material satisfying both the film flexibility requirement and the patterning resolution requirement.